Spark plug with annular ground electrode



June' 2, 1970 J, R|KHEY 7 3,515,925

SPARK PLUG WITH ANNULAR GROUND ELECTRODE w I Filed March 13, 1968 2 Sheets-Sheet l INVENTOR.

June 2,1970 .'J.R1K'n'EY --3,5 15,92 s

SPARK PLUG WITH ANNULAR fenounn ELECTRODE Filed March 15, 1968 2 Sheets-Sheet 2 FIG. 2

' INVENTOR. 2 :4 7 V 7 BY AZK United States Patent O 3,515,925 SPARK PLUG WITH ANNULAR GROUND ELECTRODE George J. Rickhey, Gelsenkirchen, Germany, assignor to Gesellschaft fiir Entwicklung und Apparatebau Dipl.- Ing. George J. Rickhey & Co. KG, Witten-Heven, Ger many 7 Filed Mar. 13, 1968, Ser. No. 712,693 Claims priority, appliccartign fiermany, May 22, 1967,

Int. (:1. H01: 13/32, 13/34 US. Cl. 313-139 16 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The present invention relates to an ignition device in general, and more particularly to a spark plug for combustion engines.

Spark plugs for combustion engines are known in a great variety of constructions. One well known construction to which the present invention is particularly applicable, comprises a center electrode which is covered by an electrical insulator in such a manner that the front end portion of the center electrode is left bare. The outer or ground electrode surrounds the electrical insulator and comprises a portion extending forwardly in form of a sleeve which surrounds the bare front end portion of the center electrode and which has an end wall provided with an axial aperture. which the bare front end portion of the center electrode extends so as to be surrounded by the apertured end wall which constitutes a ring electrode. Rearwardly of this end wall the ground electrode is sometimes provided with two diametrically opposite radial bores so that the space defined between the front end portion of the center electrode and the sleeve-like portion of the ground electrode constitutes a partially closed ignition chamber.

Compared to the more conventional types of electrodes the forementioned type has significant advantages which need be particularly described herein because they are of course well known to those skilled in the art. However, this type of electrode also has a disadvantage residing in the fact that the ejection of gas from the aforementioned ignition chamber, which must necessarily be intense for obtaining the desired uniform admixture of atomized fuel with air within the cylinder, coupled with the inevitable spark erosion, results in unacceptably high wear of material, particularly of the surface bounding the annular gap constituting the outlet of the aforementioned ignition chamber, that is the surface which defines this annular gap with the exposed portion of the center electrode.

It is therefore a general object of the present invention to overcome this disadvantage.

More particularly, it is an object of the present invention to provide an improved spark plug of the type under discussion wherein the aforementioned wear is significantly reduced while the useful lifetime of this spark plug is concomittantly significantly increased.

A further object of the invention is to provide this improvement in a simple manner and at minimum expense.

SUMMARY OF THE INVENTION In accordance with one feature of my invention I provide an ignition device particularly a spark plug of the above type for combustion engines, which comprises a center electrode having a main portion and a front end portion. An electrically insulating member surrounds the main portion of the center electrode. A ground electrode includes a sleeve having a portion surrounding the front end portion and provided with an inner circumferential face which defines with the front end portion an openended annular gap. An annulus of electrically conductive metallic material which is resistant to heat and to spark erosion, is located in this gap supported by the inner circumferential face and surrounds the front end portion of the center electrode with clearance. In accordance with my invention materials such as Wolfram, titanium, and related materials as well as alloys of such materials are particularly suitable and the employment of an annulus consisting of such materials or their alloys significantly reduces the wear of the spark plug and therefore produces a pronounced extension of their useful life. This is particularly true because the Wear of the electrodes based on spark erosion is smaller in electrodes of this type than in conventional electrodes with hook-shaped ground electrode, because in electrodes of the type here under discussion the discharge in the region of the annular gap takes place over the entire periphery of the annular gap.

It is evident that the use of the particular materials mentioned above will result in a somewhat higher expense in the construction of such spark plugs. However, the increase in useful life which is obtained in this manner for the spark plug is such that it more than compensates for the slightly higher cost. This is particularly true if the annulus consists, in accordance with a currently preferred embodiment of my invention of a press-sintered Wolfram ring, because this may be manufactured in relatively simple manner and to precisely determined tolerances, and such a ring can be precisely positioned and reliably secured in the aforementioned annular gap.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevation, in partial longitudinal section, of a spark plug embodying my invention;

FIG. 2 is a fragmentary longitudinal section on an enlarged scale of the front end portion of the electrode illustrated in FIG. 1; and

FIG. 3 is a view similar to FIG. 2 but illustrating a further embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing now the drawing in detail, and firstly FIG. 1 thereof, it will be seen that the novel spark plug according to the present invention comprises a center electrode 1 and the conventional insulating body 3, 3a of ceramic material which surrounds the electrode connecting portion 2 of the center electrode 1. A ground electrode or outer electrode 4 surrounds the insulator 3 for establishing a grounding connection with the motor cylinder in conventional manner. A polygonal portion 5 is integral with the ground electrode 4 and serves for engagement by a .tool, such as a wrench. Reference numeral- 6 identifies a deformable metallic annulus which is loosely placed over the threaded portion 4a of the ground electrode 4 and which will be deformed when the spark plug is threaded into its socket, thereby providing a reliable seal. The drawing, and specifically FIG. 1 shows that there is a slight clearance between the portion 3 of the insulating body and the ground electrode 4; however, relative axial movement is impossible because of the corresponding stepping of the two members.

The ground electrode 4, or rather the threaded portion 4a thereof is provided with an axial extension 7 which surrounds a front end portion of the center electrode 1. FIG. 2 illustrates particularly clearly that this front end portion of the center electrode 1 is not surrounded by the insulating body 3. FIG. 2 also shows that the extension 7 of the ground electrode 4 is provided with an end wall 7a which extends transversely of the elongation of the electrode and which is provided with an opening 7b into which a part of the non-insulated front end portion of the center electrode 1, which front end portion hereafter will be designated as the bare front end portion, extends. Thus, there is defined an annular gap between this bare front end portion and the surface bounding the opening 7b. I

Advantageously, although not necessarily, the portion 7 of the ground electrode 4 is provided rearwardly of the end wall 7a with two dimetrally opposite radial bores or apertures 8, 8a so that the annular space 9 located rearwardly of the end wall 7a constitutes a partly throttled ignition chamber. It will be understood that during spark discharge that portion of the fuel-air mixture contained in the chamber 9 is subjected to pre-ignition and the hot combustion gases which thereby develop are ejected through the annular gap existing between the surface 7b and the bare front end portion of the center electrode 1 in a directed stream and into the cylinder of the engine. A portion of these gases, however, will escape through the bores 8, 8a thereby reducing the kinetic energy of the axially escaping remainder and avoiding excessively-highvelocity impingement of this remainder on the bottom wall of the piston, which could result in heating of the bottom wall to impermissibly high temperatures and premature destruction of this bottom wall. Further-more, the provision of the openings 8, 8a, achieves an additional beneficial result, namely a more uniform swirlingand admixture of the fuel-air mix in the cylinder and this of course results in a more uniform and complete combustion of the mix.

In accordance with my invention the conventionally exposed surface 7b, which is subjected to considerable wear is no longer subject to such wear. To achieve this, and thereby to achieve the desired increase in the useful life of the spark plug, I interpose an annulus 10 (compare FIG. 2) between the surface 7b and the bare front end portion of the center electrode 1. This annulus 10 consists of a material which is highly heat resistant and which is also highly resistant to spark erosion. This material, which of course must have good electrical conductivity, is a metal or a metal alloy. I have found wolfram alone or in form of an alloy to be particularly suited for this purpose, although titanium and related metals are also well suited. In the embodiments disclosed herein, the annulus 10 is assumed to consist of a press-sintered wolfram material, this type of manufacture being particularly advantageous because it permits me to maintain very tight manufacturing tolerances, which are necessary to obtain satisfactory positioning of the annulus 10 as will be discussed hereafter but it also makes it possible to configurate the annulus 10 in a simple manner in whichever way is desired so as to conform its configuration to the technical requirements obtaining under given circumstances.

FIG. 2 shows that in the embodiment illustrated therein, the annulus 10 has a slight external taper, that is that its outer cross-section converges in the forward direction of the spark plug. The opening bounded by the surface 7b is provided with a complementary taper and the annulus 10 is introduced into this opening from the interior of the space 9, and is shrink-fitted in this opening so as to be tightly retained therein. In the embodiment of FIG. 2, the annulus 10 projects slightly forwardly of the outer end face of the end wall 7a, as is clearly visible.

The embodiment of FIG. 3 differs from that of FIG. 2 in that the external taper of the annulus, which in FIG. 3 is identified with'reference numeral 10a, is such that the outer cross-section of the annulus converges in opposite direction, namely in the direction inwardly towards the chamber 9. Accordingly, the taper of the surface 70, which corresponds to the surface 7b in FIG. 2, is also reversed "Sb as to conform to the taper of the annulus 1011.

In the embodiment of FIG. 3 the annulus 10a is, of course, introduced into the opening of the end wall 7a from the exterior, that is in the direction into the chamber 9 and the front end face of the annulus 10a is located in this embodiment inwardly of the front end face of the end wall 7a, rather than projecting therefrom as FIG. 2. In the embodiment of FIG. 3 the annulus 10a is held in place by upsetting the edge portion 7d bounding the opening in the end wall 7a so as to prevent axial shifting of the annulus 10a. v i I It is to be noted that the positioning of the end face of the annulus 10, 10a influences the heat value of the spark plug. In other words, the heat value of the spark plug can be varied, depending on whether the front end face of the annulus 10, 10a projects outwardly and forwardly beyond the front end face of the end wall 7a, or is recessed inwardly of this front end face. The heat value of the spark plug will be increased, and the amount of increase will be the greater, the farther the front end face of the annulus 10, projects outwardly beyond the front end face of the end wall 7a. Conversely the heat value would be decreased in proportion to the extent to which the front end face of the annulus 10a is recessed inwardly of the front end face of the end wall 7a. It is clear, of course, that the front end face of the annulus may also be flush with the front end face of the end wall 7a.

Both the annulus 10 and the annulus 10a are provided in their inner circumferential surfaces with a plurality of angularly spaced groovesll which are slightly inclined to the longitudinal axis of the respective annulus and which serve to impose upon the ejected gases a swelling movement which enhances the admixture of the fuel-air mix in the cylinder and thus provides for a more intense and more uniform admixture.

The annuli 10, 10a are each coaxial with the bare end portion of the center electrode 1, as clearly shown in FIGS. 2 and 3. A portionof their respective center apertures, generally corresponding to approximately half of the axial length thereof, is cylindrical and of substantially constant cross-section, whereas a second portion, namely that located adjacent the outlet end and identified with reference numeral 12, diverges conically and in effect constitutes a nozzle.

The center electrode 1 may consist of the materials usually employed for the manufacture of such electrodes, usually a specially-developed electrode steel, but if desired it may also consist of wolfram, titanium, or an alloy based on these metals, and it may be manufactured by press-sintering as already outlined with reference to the annuli 10,10a.

It Will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in an ignition device, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention, that others can, by applying current knowledge readily adapt it for various applications without omitting features that from the standpoint of prior art fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. An ignition device, particularly a spark plug for combustion engines, comprising in combination, a center electrode having a main portion and a front end portion having a forward end; an electrically insulating member surrounding said main portion; a ground electrode, including a sleeve having a portion smrounding said front end portion and forward end and being provided with an inner circumferential face defining with said front end portion an open-ended annular gap; at least one radial aperture in said sleeve and communicating with said annular gap; and an annulus of electrically conductive presssintered Wolfram metal resistant to heat and spark erosion, located in said gap supported by said inner circumferential face and surrounding said forward end of said front end portion with clearance.

2. A device as defined in claim 1, said inner circumferential surface diverging in the region inwardly adjacent the open end of said annular gap axially of the latter in one direction, said annulus having an outer circumferential face converging correspondingly but in direction opposite said one direction.

3. A device as defined in claim 2; and further comprising arresting means arresting said annulus against movement in said one direction.

4. A device as defined in claim 2, wherein said one direction is the direction towards the open end of said gap.

5. A device as defined in claim 2, wherein said one direction is the direction away from the open end of said gap.

6. A device as defined in claim 3, wherein said arresting means comprises an annular flange provided on said sleeve and extending radially inwardly across said gap and into engagement with said annulus for preventing axial movement of the latter.

7. A device as defined in claim 2, wherein said annulus is shrink-fitted in said gap.

8. A device as defined in claim 1, wherein said sleeve comprises an axially outwardly directed end face provided at the open end of said gap, said annulus comprising an axially outwardly directed terminal face flush with said end face.

9. A device as defined in claim 1, wherein said sleeve comprises an axially outwardly directed end face provided at the open end of said gap and having a general first plane extending transversely of the gap; said annulus comprising an axially outwardly directed end face located in a second plane parallel to said first plane.

10. A device as defined in claim 9, wherein said second plane is located axially inwardly of said first plane.

11. A device as defined in claim 9, wherein said second plane is located axially outwardly of said first plane.

12. A device as defined in claim 20, wherein at least said end portion of said center electrode is substantially rod-shaped, said annulus has a central passage comprising a first section adjacent to the open end of said gap and converging in direction inwardly thereof, and a second section inwardly adjoining said first section and being at least over part of its axial length coaxial with at least said end portion of said center electrode.

13.- A device as defined in claim 1, wherein said annulus has an inner peripheral face facing said end portions of said center electrode and being provided with a plurality of angularly spaced grooves elongated in axial direction of said annulus and slightly inclined with reference to the longitudinal axis of the latter.

14. An ignition device, particularly a spark plug for combustion engines, comprising an elongated outer electrode comprising a rear portion and a tubular front portion provided with an axial end wall having an internally tapered opening; a center electrode having a main portion located within said rear portion and a front end portion located within and defining an annular chamber with said tubular front portion, said front end portion having a leading tip provided with an outer circumferential surface; an electrically insulating member surrounding said main portion; radial aperture means in said tubular front portion and communicating with said annular chamber; and at least externally tapered annulus of electrically conductive press-sintered Wolfram metal resistant to heat and spark erosion accommodated in said opening extending transversely thereto and fixed to said tubular front portion with a shrink fit, said annulus having a forward axial end face and an inner circumferential surface which surrounds said outer circumferential surface of said leading tip and defines therewith an annular clearance including an interior clearance portion of constant cross-section and an exterior clearance portion extending from said interior portion to said axial end face and diverging in direction towards the latter; and a plurality of angularly spaced grooves provided in said inner circumferential surface elongated in axial direction of said annulus and slightly inclined with reference to the longitudinal axis of the latter.

15. An ignition device as defined in claim 14, said axial end wall having a predetermined thickness; and wherein said annulus has an axial length which is greater than said predetermined thickness.

16. An ignition device as defined in claim 15, wherein said opening tapers in direction outwardly of said tubular front portion and said annulus is externally tapered in direction opposite the taper of said opening and is received in the latter from the side of said axial end wall which faces said annular chamber.

References Cited UNITED STATES PATENTS 1,241,562 10/1917 Schmidt 313-139 X 1,313,040 8/1919 Alexander 313-139 X 1,468,929 9/1923 Strawser 313139 X 2,871,389 1/1959 Skunda 313l39 X 3,056,899 10/ 1963 Clayton 3 13-143 JAMES W. LAWRENCE, Primary Examiner C. R. CAMPBELL, Assistant Examiner US. Cl. X.R. 313-143 

